Spectral sensitive phonon wipeout due to a fluctuating spin state in a Fe2+ coordination polymer

TL;DR

This study uses Raman scattering to reveal complex spin-state transitions and phonon behavior in a Fe2+ coordination polymer, highlighting a fluctuating spin state with phonon wipeout and electron-phonon interactions.

Contribution

It uncovers a fluctuating spin state phase with phonon wipeout and demonstrates the role of electron-phonon coupling in a Fe2+ coordination polymer, supported by DFT calculations.

Findings

Identification of a fluctuating spin state with phonon wipeout.

Observation of a phase with reduced symmetry due to Jahn-Teller effect.

Detection of strong Fano-resonance indicating electron-phonon interaction.

Abstract

Raman scattering in the spin-crossover system [Fe(pmd)(H2O){Au(CN)2}2]*H2O reveals a complex three-phase spin-state transition in contrast to earlier observations in magnetization measurements. We observe different spin state phases as function of temperature and electromagnetic radiation in the visible spectral range. There exists a fluctuating spin state phase with an unexpected wipeout of the low frequency phonon scattering intensity. Furthermore we observe one phase with reduced symmetry that is attributed to a cooperative Jahn-Teller effect. Pronounced electron-phonon interaction manifests itself as a strong Fano-resonance of phonons related to {FeN6} and {FeN4O2} coordination octahedra. Density functional theory supports this interpretation.